Philippe Rigo

Maintenance/repair and production-oriented life cycle cost/earning model for ship structural optimisation during conceptual design stage

The aim of this paper is to investigate the effect of the change in structural weight due to optimisation experiments on life cycle cost and earning elements using the life cycle cost/earning model, which was developed for structure optimisation. The relation between structural variables and relevant cost/earning elements are explored and discussed in detail. The developed model is restricted to the relevant life cycle cost and earning elements, namely production cost, periodic maintenance cost, fuel oil cost, operational earning and dismantling earning. Therefore it is important to emphasise here that the cost/earning figure calculated through the developed methodology will not be a full life cycle cost/earning value for a subject vessel, but will be the relevant life cycle cost/earning value. As one of the main focuses of this paper is the maintenance/repair issue, the data was collected from a number of ship operators and was solely used for the purpose of regression analysis. An illustrative example for a chemical tanker is provided to show the applicability of the proposed approach.

A module-oriented tool for optimum design of stiffened structures—Part I

Abstract The development of the LBR-5 “Stiffened Panels Software” is included in the development of a new design methodology to ease and to improve preliminary studies of naval structures and floating hydraulic structures. The ultimate target is to link standard design tools (steel structure CAD, hull form, hydrostatic curves, floating stability, weight estimation, etc.) with a rational optimization design module and a minimum construction cost (or minimum weight) objective function. This paper is the first part of a series of two articles. It focuses on the ‘Module-Oriented Optimization’ methodology and on the rational constraints. The second paper presents the optimization technique using convex linearization and a dual approach, and the optimization of an FSO unit as an example (Rigo and Fleury, Marine Stuructures, 2001). LBR-5 allows, as of the first draft, an optimization of the scantling of the structures constituent elements. Relevant limit states of the structure are taken into account thanks to a 3D rational analysis of the structure based on the general rules of solid-mechanics and structure behaviour. The optimization module is composed of 3 basic modules (OPTI, CONSTRAINT and COST) and a group of sub-modules (in external databases). Among these the user selects a set of relevant sub-modules (i.e. geometrical and structural constraints). Since the present optimization deals with least construction costs (as objective function), and uses an explicit objective function (not empirical), the user must specify labor costs (unitary material costs, welding, cutting, etc.).

Scantling optimization based on convex linearizations and a dual approach}Part II

Abstract The development of the LBR-5 “Stiffened Panels Software” is included in the development of a new design methodology to ease and to improve preliminary studies of naval structures and floating hydraulic structures. It allows, as of the first draft, an optimization of the scantling of the structures constituent elements. The ultimate target is to link standard design tools (steel structure CAD, hull form, hydrostatic curves, floating stability, weight estimation, etc.) with a rational optimization design module and a minimum construction cost (or minimum weight) objective function. It is developed to be a user-oriented tool. The optimization module is composed of three basic modules (OPTI, CONSTRAINT and COST) and a group of sub-modules (in external databases). Among these the user selects a set of relevant sub-modules (i.e. geometrical and structural constraints). Since the present optimization deals with least construction costs (as objective function), and uses an explicit objective function (not empirical), the user must specify labor costs (unitary material costs, welding, cutting, etc.). This paper is the second part of a series of two articles. The previous paper focused on the ‘Module-Oriented Optimization’ methodology and on the rational constraints (Rigo, Marine Structures 2001). This paper presents the optimization algorithm based on convex linearization and a dual approach (OPTI module). It also includes the optimization of a FSO unit as a detailed example.

An Integrated Software for Scantling Optimization and Least Production Cost

Abstract The LBR5 package performs early design least cost optimization. The software contains a module to assesses the construction cost, a module to analyses the considered structure, and the mathematical optimizer code. The paper contains a detailed presentation of the optimization of a medium capacity LNG ship including a sensitivity analysis on frame/stiffener spacing. This industrial optimization example shows that 5-9% of the construction cost of the hull manufacturing can be saved by performing scantling optimization at the preliminary design stage.

Least cost optimization of large passenger vessels

Abstract The LBR-5 software allows optimizing ship structures according to objectives of higher inertia, less weight and/or lower cost. This last criterion offers the choice between two approaches of calculation. The first approach is based on a simplified assessment of the cost in which the total cost is described by rather simple analytical functions which bring into play on the one hand the design variables and on the other hand empirical parameters. In the second approach, the calculation of the cost is based on data specific to the shipyard. The material cost is analyzed according to the first approach while the cost of the labor considers each relevant operation of the ship building with respect to the LBR-5 model. A survey of all the tasks was carried out at Aker Yards France, and a thorough study made it possible to develop assessment tools of the labor cost for each operation as functions of the design variables. Plate straightening operations are also considered in this analysis. This paper presents a cost-based optimization study carried out on a large passenger ship structure with more than 600 design variables, by the use of the detailed approach for the cost calculation. The structural model has been formulated on the basis of technical documentation prepared by Aker Yards France. The loads and strength criteria applied on the model are considered according to classification society rules (Bureau Veritas). Results and conclusions of the study are presented.

The effects of geometrical imperfections on the ultimate strength of aluminium stiffened plates subject to combined uniaxial compression and lateral pressure

The present study aims at determining the effects of the geometrical imperfections on the ultimate strength and load-carrying capacity of aluminium stiffened plates under combined axial compression and lateral pressure. The finite element models proposed by the Committee III.1 ‘Ultimate Strength’ of ISSC’2003 are used in the present investigation. Initial imperfections as proposed by ISSC committee as well as those recommended by Ship Structure Committee are considered in the analyses. Models are tested using non-linear finite element elastic–plastic analyses. Aluminium alloy AA6082-T6 is selected as the material for the models. The studied models are triple-span panels stiffened by either extruded or non-extruded angle-bar profiles. Different arrangements of heat-affected zone (HAZ) are considered. The main outcomes of this study show the need for a subtle assessment of the real shapes of the initial deformations. The way they affect the ultimate strength of models is clarified through finite element analyses.

Numerical crashworthiness analysis of an offshore wind turbine monopile impacted by a ship

The objective of the present work is to understand the crushing behavior of a predefined wind turbine jacket when it is impacted by a ship. To investigate the resulting deformation modes and the repartition of dissipated energy, nonlinear finite element analyses are performed to simulate both rigid and deformable ships colliding the jacket at different velocities. In a first part, a sensitivity analysis to the jacket impacted area is carried out to find the most damaging situation. Then, the influences of gravity loads, wind force, and soil stiffness are studied, considering that the striking ship is rigid. In a second part, the jacket is supposed to be collided by two different deformable vessels and the internal energy distribution between the jacket and the striking ships is analyzed for different jacket leg thicknesses. Some numerical analyses focus also on the transfer of the crushing force between the impacted leg to the others through the braces. All these numerical results will further serve to fix the hypotheses for the development of a simplified tool based on analytical formulations.

Simplified Analytical Method for Estimating the Resistance of Lock Gates to Ship Impacts

The present paper is concerned with the design of lock gates submitted to ship impacts. In this paper, a simplified analytical method is presented to evaluate the resistance of such structures under collision. The basic idea is to assume that the resistance is first provided through a local deforming mode, corresponding to a localized crushing of some impacted structural elements. For consecutive larger deformations, the resistance is then mostly provided through a global deforming mode, corresponding to an overall movement of the entire gate. For assessing the resistance in the case of the local deforming mode, the structure is divided into a given number of large structural entities called “superelements.” For each of them, a relation between the resistance of the gate and the penetration of the striking ship is established. However, as some results are already available in the literature, this subject is not treated extensively in this paper. On the contrary, the calculation of the resistance of the gate provided through the global mode is detailed and the strategy to switch from local to global deformation is highlighted. Finally, we propose to validate our developments by making a comparison between results obtained numerically and those predicted by the present analytical approach.

Space and time allocation in a shipyard assembly hall

We present a space and time allocation problem that arises in assembly halls producing large building blocks (namely, a shipyard which assembles prefabricated keel elements). The building blocks are very large, and, once a block is placed in the hall, it cannot be moved until all assembly operations on this block are complete. Each block must be processed during a predetermined time window. The objective is to maximize the number of building blocks produced in the hall.The problem is modeled as a 3-dimensional bin packing problem (3D-BPP) and is handled by a Guided Local Search heuristic initially developed for the 3D-BPP. Our computational experiments with this heuristic demonstrate that excellent results can be found within minutes on a workstation. We also describe some additional real-life constraints arising in the industrial application, and we show how these constraints can be conveniently and flexibly integrated in the solution procedure.

A real-time assessment of the ship design complexity

The paper introduces an innovative complexity metric for passenger ships taking into account the shape complexity of steel parts, the assembly complexity and the material complexity. The goal is to provide the designer with such information throughout the design process so that an efficient design is obtained at the first design run. Real-time assessment of complexity and quality measurements is rather imperative to ensure efficient and effective optimality search, and to allow real-time adjustment of requirements during the design. Application and validation on a real passenger ship show that the new method is effective in giving a complementary aid to decision process for ship designers.